Dark Matter 2: In Galaxies In my last post, I talked about how galaxies seem to be rotating way fast

Dark Matter 2: In Galaxies In my last post, I talked about how galaxies seem to be rotating way faster than they should be and how we can see the effect on galaxies in detail by plotting a rotation curve. So what does this show? Well, if we use Newton’s laws to try and work out whats happening, two possible problems arise. Either Newton was wrong and his laws don’t work on a galactic scale, or our calculations of galactic mass are way off. At this point in time the second problem seems to be more realistic, but I’ll go into more detail in a future post :) So galaxies seem to be too light, but where does dark matter fit into this? Well we could say that maybe there is some stuff in the galaxy that we can’t see, and that it is much heavier than the stuff stars and gas are made of, then the problem is solved. This is the basic definition of dark matter, and it is the theory that most astrophysicists use today. In the rotation curve of the galaxy in the last post, it was clear that the further you move away from the centre of the galaxy, the faster the stars and gas rotate. The image I have included today shows how the dark matter forms a ‘halo’ pattern rotating around the galaxy. This matches Newton’s law: more mass, faster speed. So this solves both problems doesn’t it? Galaxies are heavier, so Newton’s law can be used. Right? Well, we don’t know. In fact we haven’t found any evidence of a dark matter particle existing. So is there any other evidence? Can we find dark matter anywhere else? More to come in the next post! -- source link

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